Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$29.61	11.121%	$32.9029	$32.90	$32.90	$32.90
Purchase #2	$35.76	5.317%	$37.6614	$37.66	$37.65	$37.70
Purchase #3	$173.87	9.246%	$189.946	$189.95	$189.95	$189.90
Purchase #4	$136.48	3.500%	$141.2568	$141.26	$141.25	$141.30
Purchase #5	$204.57	7.166%	$219.2295	$219.23	$219.25	$219.20
Purchase #6	$86.76	9.499%	$95.0013	$95.00	$95.00	$95.00
Purchase #7	$222.41	9.657%	$243.8881	$243.89	$243.90	$243.90
7 purchase totals =	$889.46		$959.8860	$959.89	$959.90	$959.90